The Data Over Cable Service Interface Specification (DOCSIS) standard defines a high speed, bi-directional, data communication channel between cable providers and cable customers. The DOCSIS standard defines the layer 1 thru layer 3 communication protocols, timings, and Radio Frequency (RF) specifications for data traffic over cable systems. The communication media can be either coaxial cable or fiber.
FIG. 1 shows how Internet Protocol (IP) traffic is currently transferred over a DOCSIS system. A communication link is established between a Cable Modem Termination Systems (CMTS) 14 on the cable provider end and a Cable Modem (CM) 20 on the customer premises. Data transfers from the CMTS 14 to the CM 20 are referred to as downstream while transfers from the CM 20 to the CMTS 14 are referred to as upstream.
The CMTS 14 at a cable system headend may include a Wide Area Network connection 12, such as an Ethernet connection, that receives IP traffic. Other types of network interfaces may also be used such as Dynamic Packet Transport/Resilient Packet Ring (DPT/RPR) or Packet-over-SONET/SDH (POS) The CMTS 14 modulates the IP traffic over a single downstream channel 16 on a high speed Hybrid Fiber Coax (HFC) 19. In one instance, the single downstream channel 16 has a bandwidth limit of about 30 to 42 Million Bits Per Second (Mbps) and may supply downstream IP connectivity for up to 8000 different cable modems 20 connected to the same cable plant 19. Each cable modem 20 demodulates the downstream traffic and formats the traffic for transfer over Ethernet link 22. Upstream IP traffic is transferred over upstream channel 18.
Most cable traffic consists of data flowing in the downstream direction from CMTS 14 to CM 20. Current bandwidth may be sufficient for large numbers of cable modems with bursty traffic that can operate efficiently on shared bandwidth. However, current cable systems cannot support applications that have a high average bandwidth such as Constant Bit Rate (CBR) or Variable Bit Rate (VBR) Video.
The present invention addresses this and other problems associated with the prior art.